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1.
We assessed the effects of doubling atmospheric CO2 concentration, [CO2], on C and N allocation within pedunculate oak plants (Quercus robur L.) grown in containers under optimal water supply. A short-term dual 13CO2 and 15NO3? labelling experiment was carried out when the plants had formed their third growing flush. The 22-week exposure to 700 μl l?1 [CO2] stimulated plant growth and biomass accumulation (+53% as compared with the 350 μl l?1 [CO2] treatment) but decreased the root/shoot biomass ratio (-23%) and specific leaf area (-18%). Moreover, there was an increase in net CO2 assimilation rate (+37% on a leaf dry weight basis; +71% on a leaf area basis), and a decrease in both above- and below-ground CO2 respiration rates (-32 and -26%, respectively, on a dry mass basis) under elevated [CO2]. 13C acquisition, expressed on a plant mass basis or on a plant leaf area basis, was also markedly stimulated under elevated [CO2] both after the 12-h 13CO2 pulse phase and after the 60-h chase phase. Plant N content was increased under elevated CO2 (+36%), but not enough to compensate for the increase in plant C content (+53%). Thus, the plant C/N ratio was increased (+13%) and plant N concentration was decreased (-11%). There was no effect of elevated [CO2] on fine root-specific 15N uptake (amount of recently assimilated 15N per unit fine root dry mass), suggesting that modifications of plant N pools were merely linked to root size and not to root function. N concentration was decreased in the leaves of the first and second growing flushes and in the coarse roots, whereas it was unaffected by [CO2] in the stem and in the actively growing organs (fine roots and leaves of the third growth flush). Furthermore, leaf N content per unit area was unaffected by [CO2]. These results are consistent with the short-term optimization of N distribution within the plants with respect to growth and photosynthesis. Such an optimization might be achieved at the expense of the N pools in storage compartments (coarse roots, leaves of the first and second growth flushes). After the 60-h 13C chase phase, leaves of the first and second growth flushes were almost completely depleted in recent 13C under ambient [CO2], whereas these leaves retained important amounts of recently assimilated 13C (carbohydrate reserves?) under elevated [CO2].  相似文献   

2.
Few studies have investigated how tree species grown under elevated CO2 and elevated temperature alter the performance of leaf‐feeding insects. The indirect effects of an elevated CO2 concentration and temperature on leaf phytochemistry, along with potential direct effects on insect growth and consumption, may independently or interactively affect insects. To investigate this, we bagged larvae of the gypsy moth on leaves of red and sugar maple growing in open‐top chambers in four CO2/temperature treatment combinations: (i) ambient temperature, ambient CO2; (ii) ambient temperature, elevated CO2 (+ 300 μL L?1 CO2); (iii) elevated temperature (+ 3.5°C), ambient CO2; and (iv) elevated temperature, elevated CO2. For both tree species, leaves grown at elevated CO2 concentration were significantly reduced in leaf nitrogen concentration and increased in C: N ratio, while neither temperature nor its interaction with CO2 concentration had any effect. Depending on the tree species, leaf water content declined (red maple) and carbon‐based phenolics increased (sugar maple) on plants grown in an enriched CO2 atmosphere. The only observed effect of elevated temperature on leaf phytochemistry was a reduction in leaf water content of sugar maple leaves. Gypsy moth larval responses were dependent on tree species. Larvae feeding on elevated CO2‐grown red maple leaves had reduced growth, while temperature had no effect on the growth or consumption of larvae. No significant effects of either temperature or CO2 concentration were observed for larvae feeding on sugar maple leaves. Our data demonstrate strong effects of CO2 enrichment on leaf phytochemical constituents important to folivorous insects, while an elevated temperature largely has little effect. We conclude that alterations in leaf chemistry due to an elevated CO2 atmosphere are more important in this plant–folivorous insect system than either the direct short‐term effects of temperature on insect performance or its indirect effects on leaf chemistry.  相似文献   

3.
Image sequence processing methods were applied to study the effect of elevated CO2 on the diel leaf growth cycle for the first time in a dicot plant. Growing leaves of Populus deltoides, in stands maintained under ambient and elevated CO2 for up to 4 years, showed a high degree of heterogeneity and pronounced diel variations of their relative growth rate (RGR) with maxima at dusk. At the beginning of the season, leaf growth did not differ between treatments. At the end of the season, final individual leaf area and total leaf biomass of the canopy was increased in elevated CO2. Increased final leaf area at elevated CO2 was achieved via a prolonged phase of leaf expansion activity and not via larger leaf size upon emergence. The fraction of leaves growing at 30–40% day?1 was increased by a factor of two in the elevated CO2 treatment. A transient minimum of leaf expansion developed during the late afternoon in leaves grown under elevated CO2 as the growing season progressed. During this minimum, leaves grown under elevated CO2 decreased their RGR to 50% of the ambient value. The transient growth minimum in the afternoon was correlated with a transient depletion of glucose (less than 50%) in the growing leaf in elevated CO2, suggesting diversion of glucose to starch or other carbohydrates, making this substrate temporarily unavailable for growth. Increased leaf growth was observed at the end of the night in elevated CO2. Net CO2 exchange and starch concentration of growing leaves was higher in elevated CO2. The extent to which the transient reduction in diel leaf growth might dampen the overall growth response of these trees to elevated CO2 is discussed.  相似文献   

4.
Atmospheric change may affect plant phenolic compounds, which play an important part in plant survival. Therefore, we studied the impacts of CO2 and O3 on the accumulation of 27 phenolic compounds in the short‐shoot leaves of two European silver birch (Betula pendula Roth) clones (clones 4 and 80). Seven‐year‐old soil‐grown trees were exposed in open‐top chambers over three growing seasons to ambient and twice ambient CO2 and O3 concentrations singly and in combination in central Finland. Elevated CO2 increased the concentration of the phenolic acids (+25%), myricetin glycosides (+18%), catechin derivatives (+13%) and soluble condensed tannins (+19%) by increasing their accumulation in the leaves of the silver birch trees, but decreased the flavone aglycons (?7%) by growth dilution. Elevated O3 increased the concentration of 3,4′‐dihydroxypropiophenone 3‐β‐d ‐glucoside (+22%), chlorogenic acid (+19%) and flavone aglycons (+4%) by inducing their accumulation possibly as a response to increased oxidative stress in the leaf cells. Nevertheless, this induction of antioxidant phenolic compounds did not seem to protect the birch leaves from detrimental O3 effects on leaf weight and area, but may have even exacerbated them. On the other hand, elevated CO2 did seem to protect the leaves from elevated O3 because all the O3‐derived effects on the leaf phenolics and traits were prevented by elevated CO2. The effects of the chamber and elevated CO2 on some compounds changed over time in response to the changes in the leaf traits, which implies that the trees were acclimatizing to the altered environmental conditions. Although the two clones used possessed different composition and concentrations of phenolic compounds, which could be related to their different latitudinal origin and physiological characteristics, they responded similarly to the treatments. However, in some cases the variation in phenolic concentrations caused by genotype or chamber environment was much larger than the changes caused by either elevated CO2 or O3.  相似文献   

5.
The impact of elevated CO2 (1000 μmol/mol) was assessed on the common weed,Arabidopsis thaliana (Landsberg erecta), which is used as a model plant system. Elevated CO2 stimulated relative growth rate (RGR) and leaf area gain ofArabidopsis beginning from the cotyledon stage and continuing through the juvenile stage. This early advantage in growth enabled the plants grown in elevated CO2 to gain more DW despite similar RGRs throughout the latter stages of development. The greater accumulation of DW in leaves grown in elevated CO2 resulted in a lower specific leaf area (SLA). However, the amount of cell wall investment per unit of leaf area, specific “wall” area (SWA), was similar indicating that elevated CO2 did not affect the distribution of cell carbon to the cell wall of leaves beyond that needed for cell and leaf expansion. Furthermore, cell wall composition changed with time due to developmental changes and was not affected by elevated CO2. Associated with the increase in RGR by elevated CO2 was a concomitant increase in the activity of UDP-Glc dehydrogenase (E.C. 1.1.1.22), a key enzyme in the nucleotide-sugar interconversion pathway necessary for biosynthesis of many cell-wall polysaccharides.  相似文献   

6.
The effects of elevated CO2 on plant growth and insect herbivory have been frequently investigated over the past 20 years. Most studies have shown an increase in plant growth, a decrease in plant nitrogen concentration, an increase in plant secondary metabolites and a decrease in herbivory. However, such studies have generally overlooked the fact that increases in plant production could cause increases of herbivores per unit area of habitat. Our study investigated leaf production, herbivory levels and herbivore abundance per unit area of leaf litter in a scrub‐oak system at Kennedy Space Center, Florida, under conditions of ambient and elevated CO2, over an 11‐year period, from 1996 to 2007. In every year, herbivory, that is leafminer and leaftier abundance per 200 leaves, was lower under elevated CO2 than ambient CO2 for each of three species of oaks, Quercus myrtifolia, Quercus chapmanii and Quercus geminata. However, leaf litter production per 0.1143 m2 was greater under elevated CO2 than ambient CO2 for Q. myrtifolia and Q. chapmanii, and this difference increased over the 11 years of the study. Leaf production of Q. geminata under elevated CO2 did not increase. Leafminer densities per 0.1143 m2 of litterfall for Q. myrtifolia and Q. chapmanii were initially lower under elevated CO2. However, shortly after canopy closure in 2001, leafminer densities per 0.1143 m2 of litter fall became higher under elevated CO2 and remained higher for the remainder of the experiment. Leaftier densities per 0.1143 m2 were also higher under elevated CO2 for Q. myrtifolia and Q. chapmanii over the last 6 years of the experiment. There were no differences in leafminer or leaftier densities per 0.1143 m2 of litter for Q. geminata. These results show three phenomena. First, they show that elevated CO2 decreases herbivory on all oak species in the Florida scrub‐oak system. Second, despite lower numbers of herbivores per 200 leaves in elevated CO2, increased leaf production resulted in higher herbivore densities per unit area of leaf litter for two oak species. Third, they corroborate other studies which suggest that the effects of elevated CO2 on herbivores are species specific, meaning they depend on the particular plant species involved. Two oak species showed increases in leaf production and herbivore densities per 0.1143 m2 in elevated CO2 over time while another oak species did not. Our results point to a future world of elevated CO2 where, despite lower plant herbivory, some insect herbivores may become more common.  相似文献   

7.
In autumn, agricultural perennial weeds prepare for winter and can store reserves into creeping roots or rhizomes. Little is known about influence of climate change in this period. We tested the effect of simulated climate change in autumn on three widespread and noxious perennial weeds, Elymus repens (L.) Gould, Cirsium arvense (L.) Scop. and Sonchus arvensis L. We divided and combined simulated climate change components into elevated CO2 concentration (525 ppm), elevated temperatures (+2–2.5°C), treatments in open‐top chambers. In addition, a control in the open‐top chamber without any increase in CO2 and temperature, and a field control outside the chambers were included. Two geographically different origins and three pre‐growth periods prior to the exposure to climate change factors were included for each species. All species increased leaf area under elevated temperature, close to doubling in E. repens and quadrupling in the dicot species. E. repens kept leaves green later in autumn. C. arvense did not benefit in below‐ground growth from more leaf area or leaf dry mass. S. arvensis had low levels of leaf area throughout the experiment and withered earlier than the two other species. Below‐ground plant parts of S. arvensis were significantly increased by elevated temperature. Except for root:shoot ratio of C. arvense, the effects of pure elevated CO2 were not significant for any variables compared to the open‐top chamber control. There was an additive, but no synergistic, effect of enhanced temperature and CO2. The length of pre‐growth period was highly important for autumn plant growth, while origin had minor effect. We conclude that the small transfer of enhanced above‐ground growth into below‐ground growth under climate change in autumn does not favour creeping perennial plants per se, but more leaf area may offer more plant biomass to be tackled by chemical or physical weed control.  相似文献   

8.
First, we report the results of the longest‐known field study (9 years) to examine the effects of elevated carbon dioxide (CO2) on leaf miner densities in a scrub‐oak community at Kennedy Space Center, Florida. Here, the densities of all leaf miner species (6) on all host species (3) were lower in every year in elevated CO2 than they were in ambient CO2. Second, meta‐analyses were used to review the effects of elevated CO2 on both plants (n=59 studies) and herbivores (n=75 studies). The log of the response ratio was chosen as the metric to calculate effect sizes. Results showed that elevated CO2 significantly decreased herbivore abundance (−21.6%), increased relative consumption rates (+16.5%), development time (+3.87%) and total consumption (+9.2%), and significantly decreased relative growth rate (−8.3%), conversion efficiency (−19.9%) and pupal weight (−5.03%). No significant differences were observed among herbivore guilds. Host plants growing under enriched CO2 environments exhibited significantly larger biomass (+38.4%), increased C/N ratio (+26.57%), and decreased nitrogen concentration (−16.4%), as well as increased concentrations of tannins (+29.9%) and other phenolics. Effects of changes on plant primary and secondary chemistry due to elevated CO2 and consequences for herbivore growth and development are discussed.  相似文献   

9.
Growth in elevated CO2 often leads to decreased plant nitrogen contents and down-regulation of photosynthetic capacity. Here, we investigated whether elevated CO2 limits nitrogen uptake when nutrient movement to roots is unrestricted, and the dependence of this limitation on nitrogen supply and plant development in durum wheat (Triticum durum Desf.). Plants were grown hydroponically at two N supplies and ambient and elevated CO2 concentrations. Elevated CO2 decreased nitrate uptake per unit root mass with low N supply at early grain filling, but not at anthesis. This decrease was not associated with higher nitrate or amino acid, or lower non-structural carbohydrate contents in roots. At anthesis, elevated CO2 decreased the nitrogen content of roots with both levels of N and that of aboveground organs with high N. With low N, elevated CO2 increased N allocation to aboveground plant organs and nitrogen concentration per unit flag leaf area at anthesis, and per unit aboveground dry mass at both growth stages. The results from the hydroponic experiment suggest that elevated CO2 restricts nitrate uptake late in development, high N supply overriding this restriction. Increased nitrogen allocation to young leaves at low N supply could alleviate photosynthetic acclimation to elevated CO2.  相似文献   

10.
By affecting plant growth and phytochemistry elevated CO2 may have indirect effects on the performance of herbivores. These effects show considerable variability across studies and may depend on nutrient availability, the carbon/nutrient‐balance in plant tissues and the secondary metabolism of plants. We studied the responses to elevated CO2 and different nutrient availability of 12 herbaceous plant species differing in their investment into secondary compounds. Caterpillars of the generalist herbivore Spodoptera littoralis were reared on the leaves produced and their consumption and growth rates analysed. Elevated CO2 resulted in a similar increase of biomass in all plant species, whereas the positive effect of fertilization varied among plant species. Specific leaf weight was influenced by elevated CO2, but the effect depended on nutrient level and identity of plant species. Elevated CO2 increased the C/N ratio of the leaves of most species. Caterpillars consumed more leaf material when plants were grown under elevated CO2 and low nutrients. This indicates compensatory feeding due to lower tissue quality. However, the effects of elevated CO2, nutrient availability and plant species identity on leaf consumption interacted. Both the effects of CO2 and nutrient availability on the relative growth rate of the herbivore depended on the plant species. The feeding rate of S. littoralis on plant species that do not produce nitrogen‐containing secondary compounds (NCSC) was higher under low nutrient availability. In contrast, in plants producing NCSC nutrient availability had no effect on the feeding rate. This suggests that compensatory feeding in response to low nutrient contents may not be possible if plants produce NCSC. We conclude that elevated CO2 causes species‐specific changes in the quality of plant tissues and consequently in changes in the preferences of herbivores for plant species. This could result in changes in plant community composition.  相似文献   

11.
Poplar (Populus × euroamericana) saplings were grown in the field to study the changes of photosynthesis and isoprene emission with leaf ontogeny in response to free air carbon dioxide enrichment (FACE) and soil nutrient availability. Plants growing in elevated [CO2] produced more leaves than those in ambient [CO2]. The rate of leaf expansion was measured by comparing leaves along the plant profile. Leaf expansion and nitrogen concentration per unit of leaf area was similar between nutrient treatment, and this led to similar source–sink functional balance. Consequently, soil nutrient availability did not cause downward acclimation of photosynthetic capacity in elevated [CO2] and did not affect isoprene synthesis. Photosynthesis assessed in growth [CO2] was higher in plants growing in elevated than in ambient [CO2]. After normalizing for the different number of leaves over the profile, maximal photosynthesis was reached and started to decline earlier in elevated than in ambient [CO2]. This may indicate a [CO2]‐driven acceleration of leaf maturity and senescence. Isoprene emission was adversely affected by elevated [CO2]. When measured on the different leaves of the profile, isoprene peak emission was higher and was reached earlier in ambient than in elevated [CO2]. However, a larger number of leaves was emitting isoprene in plant growing in elevated [CO2]. When integrating over the plant profile, emissions in the two [CO2] levels were not different. Normalization as for photosynthesis showed that profiles of isoprene emission were remarkably similar in the two [CO2] levels, with peak emissions at the centre of the profile. Only the rate of increase of the emission of young leaves may have been faster in elevated than in ambient [CO2]. Our results indicate that elevated [CO2] may overall have a limited effect on isoprene emission from young seedlings and that plants generally regulate the emission to reach the maximum at the centre of the leaf profile, irrespective of the total leaf number. In comparison with leaf expansion and photosynthesis, isoprene showed marked and repeatable differences among leaves of the profile and may therefore be a useful trait to accurately monitor changes of leaf ontogeny as a consequence of elevated [CO2].  相似文献   

12.
The anatomical features of leaves in 11 species of plants grown in a temperature gradient and a temperature + CO2 gradient were studied. The palisade parenchyma thickness, the spongy parenchyma thickness and the total leaf thickness were measured and analyzed to investigate the effects of elevated temperature and CO2 on the anatomical characteristics of the leaves. Our results show that with the increase of temperature, the leaf thickness of C4 species increased while the leaf thickness of C3 species showed no constant changes. With increased CO2, seven out of nine C3 species exhibited increased total leaf thickness. In C4 species, leaf thickness decreased. As for the trend on the multi-grades, the plants exhibited linear or non-linear changes. With the increase of temperature or both temperature and CO2 for the 11 species investigated, leaf thickness varied greatly in different plants (species) and even in different branches on the same plant. These results demonstrated that the effect of increasing CO2 and temperature on the anatomical features of the leaves were species-specific. Since plant structures are correlated with plant functions, the changes in leaf anatomical characteristics in elevated temperature and CO2 may lead to functional differences. Translated from Acta Ecologica Sinica, 2006, 26(2): 326–333 [译自: 生态学报]  相似文献   

13.
Strengbom J  Reich PB 《Oecologia》2006,149(3):519-525
To evaluate whether leaf spot disease and related effects on photosynthesis are influenced by increased nitrogen (N) input and elevated atmospheric CO2 concentration ([CO2]), we examined disease incidence and photosynthetic rate of Solidago rigida grown in monoculture under ambient or elevated (560 μmol mol−1) [CO2] and ambient or elevated (+4 g N m−2 year−1) N conditions in a field experiment in Minnesota, USA. Disease incidence was lower in plots with either elevated [CO2] or enriched N (−57 and −37%, respectively) than in plots with ambient conditions. Elevated [CO2] had no significant effect on total plant biomass, or on photosynthetic rate, but reduced tissue%N by 13%. In contrast, N fertilization increased both biomass and total plant N by 70%, and as a consequence tissue%N was unaffected and photosynthetic rate was lower on N fertilized plants than on unfertilized plants. Regardless of treatment, photosynthetic rate was reduced on leaves with disease symptoms. On average across all treatments, asymptomatic leaf tissue on diseased leaves had 53% lower photosynthetic rate than non-diseased leaves, indicating that the negative effect from the disease extended beyond the visual lesion area. Our results show that, in this instance, indirect effects from elevated [CO2], i.e., lower disease incidence, had a stronger effect on realized photosynthetic rate than the direct effect of higher [CO2].  相似文献   

14.
The anatomical features of leaves in 11 species of plants grown in a temperature gradient and a temperature + CO2 gradient were studied. The palisade parenchyma thickness, the spongy parenchyma thickness and the total leaf thickness were measured and analyzed to investigate the effects of elevated temperature and CO2 on the anatomical characteristics of the leaves. Our results show that with the increase of temperature, the leaf thickness of C4 species increased while the leaf thickness of C3 species showed no constant changes. With increased CO2, seven out of nine C3 species exhibited increased total leaf thickness. In C4 species, leaf thickness decreased. As for the trend on the multi-grades, the plants exhibited linear or non-linear changes. With the increase of temperature or both temperature and CO2 for the 11 species investigated, leaf thickness varied greatly in different plants (species) and even in different branches on the same plant. These results demonstrated that the effect of increasing CO2 and temperature on the anatomical features of the leaves were species-specific. Since plant structures are correlated with plant functions, the changes in leaf anatomical characteristics in elevated temperature and CO2 may lead to functional differences.  相似文献   

15.
Impacts of either elevated CO2 or drought stress on plant growth have been studied extensively, but interactive effects of these on plant carbon and nitrogen allocation is inadequately understood yet. In this study the response of the dominant desert shrub, Caragana intermedia Kuanget H.c.Fu, to the interaction of elevated CO2 (700 ± 20 μmol mol−1) and soil drought were determined in two large environmental growth chambers (18 m2). Elevated CO2 increased the allocation of biomass and carbon into roots and the ratio of carbon to nitrogen (C:N) as well as the leaf soluble sugar content, but decreased the allocation of biomass and carbon into leaves, leaf nitrogen and leaf soluble protein concentrations. Elevated CO2 significantly decreased the partitioning of nitrogen into leaves, but increased that into roots, especially under soil drought. Elevated CO2 significantly decreased the carbon isotope discrimination (Δ) in leaves, but increased them in roots, and the ratio of Δ values between root and leaf, indicating an increased allocation into below-ground parts. It is concluded that stimulation of plant growth by CO2 enrichment may be negated under soil drought, and under the future environment, elevated CO2 may partially offset the negative effects of enhanced drought by regulating the partitioning of carbon and nitrogen.  相似文献   

16.
Plant species differ broadly in their responses to an elevated CO2 atmosphere, particularly in the extent of nitrogen dilution of leaf tissue. Insect herbivores are often limited by the availability of nutrients, such as nitrogen, in their host plant tissue and may therefore respond differentially on different plant species grown in CO2-enriched environments. We reared gyspy moth larvae (Lymantria dispar) in situ on seedlings of yellow birch (Betula allegheniensis) and gray birch (B. populifolia) grown in an ambient (350 ppm) or elevated (700 ppm) CO2 atmosphere to test whether larval responses in the elevated CO2 atmosphere were species-dependent. We report that female gypsy moths (Lymantria dispar) reared on gray birch (Betula populifolia) achieved similar pupal masses on plants grown at an ambient or an elevated CO2 concentration. However, on yellow birch (B. allegheniensis), female pupal mass was 38% smaller on plants in the elevated-CO2 atmosphere. Larval mortality was significantly higher on yellow birch than gray birch, but did not differ between the CO2 treatments. Relative growth rate declined more in the elevated CO2 atmosphere for larvae on yellow birch than for those on gray birch. In preference tests, larvae preferred ambient over elevated CO2-grown leaves of yellow birch, but showed no preference between gray birch leaves from the two CO2 atmospheres. This differential response of gypsy moths to their host species corresponded to a greater decline in leaf nutritional quality in the elevated CO2 atmosphere in yellow birch than in gray birch. Leaf nitrogen content of yellow birch dropped from 2.68% to 1.99% while that of gray birch leaves only declined from 3.23% to 2.63%. Meanwhile, leaf condensed tannin concentration increased from 8.92% to 11.45% in yellow birch leaves while gray birch leaves only increased from 10.72% to 12.34%. Thus the declines in larval performance in a future atmosphere may be substantial and host-species-specific.  相似文献   

17.
Determining underlying physiological patterns governing plant productivity and diversity in grasslands are critical to evaluate species responses to future environmental conditions of elevated CO2 and nitrogen (N) deposition. In a 9‐year experiment, N was added to monocultures of seven C3 grassland species exposed to elevated atmospheric CO2 (560 μmol CO2 mol?1) to evaluate how N addition affects CO2 responsiveness in species of contrasting functional groups. Functional groups differed in their responses to elevated CO2 and N treatments. Forb species exhibited strong down‐regulation of leaf Nmass concentrations (?26%) and photosynthetic capacity (?28%) in response to elevated CO2, especially at high N supply, whereas C3 grasses did not. Hence, achieved photosynthetic performance was markedly enhanced for C3 grasses (+68%) in elevated CO2, but not significantly for forbs. Differences in access to soil resources between forbs and grasses may distinguish their responses to elevated CO2 and N addition. Forbs had lesser root biomass, a lower distribution of biomass to roots, and lower specific root length than grasses. Maintenance of leaf N, possibly through increased root foraging in this nutrient‐poor grassland, was necessary to sustain stimulation of photosynthesis under long‐term elevated CO2. Dilution of leaf N and associated photosynthetic down‐regulation in forbs under elevated [CO2], relative to the C3 grasses, illustrates the potential for shifts in species composition and diversity in grassland ecosystems that have significant forb and grass components.  相似文献   

18.
CO2 responsiveness of plants: a possible link to phloem loading   总被引:5,自引:3,他引:2  
Of the many responses of plants to elevated CO2, accumulation of total non-structural carbohydrates (TNC in % dry weight) in leaves is one of the most consistent. Insufficient sink activity or transport capacity may explain this obvious disparity between CO2 assimilation and carbohydrate dissipation and structural investment. If transport capacity contributes to the problem, phloem loading may be the crucial step. It has been hypothesized that symplastic phloem loading is less efficient than apoplastic phloem loading, and hence plant species using the symplastic pathway and growing under high light and good water supply should accumulate more TNC at any given CO2 level, but particularly under elevated CO2. We tested this hypothesis by carrying out CO2 enrichment experiments with 28 plant species known to belong to groups of contrasting phloem-loading type. Under current ambient CO2 symplastic loaders were found to accumulate 36% TNC compared with only 19% in apoplastic loaders (P=0.0016). CO2 enrichment to 600 μmol mol?1 increased TNC in both groups by the same absolute amount, bringing the mean TNC level to 41% in symplastic loaders (compared to 25% in apoplastic loaders), which may be close to TNC saturation (coupled with chlornplast malfunction). Eight tree species, ranked as symplastic loaders by their minor vein companion cell configuration, showed TNC responses more similar to those of apoplastic herbaceous loaders. Similar results are obtained when TNC is expressed on a unit leaf area basis, since mean specific leaf areas of groups were not significantly different. We conclude that phloem loading has a surprisingly strong effect on leaf tissue composition, and thus may translate into alterations of food webs and ecosystem functioning, particularly under high CO2.  相似文献   

19.
Concentration of atmospheric CO2 and temperature have both been rising for the last three decades. In this century, the temperature has been predicted to rise by 2–5 °C and the CO2 concentration to double. These changes may affect the primary and secondary metabolism of plants and thus have implications for other trophic levels. However, the biotic interactions in changing climate conditions are poorly known. In this study, two questions were addressed: (i) How will climate change affect growth and the amounts of secondary compounds in flexible plant species? and (ii) How will this affect herbivores living on this species. Four clones of the dark‐leaved willow (Salix myrsinifolia (Salisb.)) seedlings were grown in closed‐top chambers with two controlled factors: concentration of atmospheric CO2 and temperature (T). There were four combinations of these factors, each combination replicated four times (total of 16 chambers): (i) Control CO2 (350 ppm) and control T, (ii) Elevated CO2 (700 ppm) and control T, (iii) Control CO2 and elevated T (2 °C), and (iv) Elevated CO2 and elevated T. Stem growth and aerial biomass of the plants were determined; and the leaf phenolics, nitrogen and water concentrations were analysed. In addition the growth rate of larvae and feeding preference of adults of a specialist herbivore, the chrysomelid beetle Phratora vitellinae (L.), on the treated willow leaves were measured. Elevated temperature and CO2 concentration increased the stem biomass and elevated CO2 increased leaf biomass and total aerial biomass of the willows. Patterns of biomass allocation were different in different temperature treatments. At elevated temperature there was less branch and leaf material in relation to stems than at the control temperature. Moreover, patterns of biomass allocation differed among clones. CO2 enhancement increased the specific leaf weight (SLW) and reduced both water and nitrogen content of the leaves, however, leaf area was unaffected by the treatments. Carbon dioxide (CO2) and T enhancement reduced the concentrations of several phenolic compounds in the leaves. Phenolic compounds, nutrients, and water in the leaves might be diluted partly due to increased carbon allocation to different structures (e.g. thickening of cell wall and increase of trichomes, etc.). In some cases plant clones showed specific responses to treatments. The CO2 enhancement reduced the relative growth rate (RGR) of the beetle larvae, and in contrast, temperature elevation increased it. Adult beetles did not clearly discriminate between willow leaves grown in different T and CO2 environments, but tended to eat more leaf material from chambers with doubled CO2 concentration. At elevated CO2 adult beetles may need to eat more leaf material in order to reproduce, which may in turn prolong the life cycles, increasing the risk of being eaten and possibly affecting ability to overwinter successfully. Overall, climate change may significantly modify the dynamic interaction between willow and beetle populations.  相似文献   

20.
Small birch plants (Betula pendula Roth.) were grown from seed for periods of up to 70d in a climate chamber at optimal nutrition and at present (350 μmol mol?1) or elevated (700 μmol mol?1) concentrations of atmospheric CO2. Nutrients were sprayed over the roots in Ingestad-type units. Relative growth rate and net assimilation rate were slightly higher at elevated CO2, whereas leaf area ratio was slightly lower. Smaller leaf area ratio was associated with lower values of specific leaf area. Leaves grown at elevated CO2 had higher starch concentrations (dry weight basis) than leaves grown at present levels of CO2. Biomass allocation showed no change with CO2, and no large effects on stem height, number of side shoots and number of leaves were found. However, the specific root length of fine roots was higher at elevated CO2. No large difference in the response of carbon assimilation to intercellular CO2 concentration (A/Ci curves) were found between CO2 treatments. When measured at the growth environments, the rates of photosynthesis were higher in plants grown at elevated CO2 than in plants grown at present CO2. Water use efficiency of single leaves was higher in the elevated treatment. This was mainly attributable to higher carbon assimilation rate at elevated CO2. The difference in water use efficiency diminished with leaf age. The small treatment difference in relative growth rate was maintained throughout the experiment, which meant that the difference in plant size became progressively greater. Thus, where plant nutrition is sufficient to maintain maximum growth, small birch plants may potentially increase in size more rapidly at elevated CO2.  相似文献   

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